The carnage continues at the Sydney International, with reigning US Open champion Sloane Stephens crashing out in a first-round rout lasting barely an hour.

Italian qualifier Camila Giorgi swatted aside sixth-seeded Stephens 6-3, 6-0 in 65 minutes to book a potential second-round showdown with dual Wimbledon champion Petra Kvitova.

Stephens' swift exit in her first tournament of the year leaves the world No.13 alarmingly underdone heading into next week's Australian Open in Melbourne.

But the 24-year-old is by no means the only big-name women's player showing a lack of form entering the season-opening grand slam.

French Open champion Jelena Ostapenko, the world No.7, and the 11th-ranked Kristina Mladenovic also both bombed out in the first round in Sydney.

Seventh seed Anastasija Sevastova is also on her way to Melbourne after falling 6-3, 6-1 to former Australian Open finalist Dominika Cibulkova in her opening match on Monday.

In Hobart, former world No.5 Eugenie Bouchard was ousted in the opening round.

Heavy-hitting Belarusian teen Aryna Sabalenka on Monday eliminated the wildcard and 2016 Hobart finalist 6-4, 6-3.

It leaves Bouchard winless in her Aussie campaign, having dropped all three singles matches at last week's Hopman Cup.

The former Wimbledon finalist withdrew from her last mixed doubles match in Perth with a buttock injury but insisted that wasn't causing her any ongoing problems.

"It's not where I want to be," she said of her recent form after hitting 12 double faults in her loss to the 19-year-old Sabalenka.

"But I'll just take away another match as part of the learning process and just keep going.

Australia's big summer hope Ashleigh Barty posted her first win of the summer, grinding out a 6-3, 6-4 victory over Paraguayan qualifier Veronica Cepede Royg in Sydney to draw a line under last week's first-round loss last week in Brisbane.

The world No.19 next faces Sydney wildcard Ellen Perez, ensuring at least one Australian in the quarter-finals.

Angelique Kerber's first-round clash with Lucie Safarova has been halted for a second time due to lightning and heavy rain.

The German former world No.1 had just gone down in the first set 7-6 (7-3) when booming cracks of thunder forced organisers to suspend play.

The winner will set up a second-round date with seven-times major winner Venus Williams on Tuesday evening.

AAP